Photochromic properties calculation of diaryl maleic anhydride

Abstract In the calculation of the photochromic mechanism of (2,3-di(3-furyl)maleic anhydride, DFMA) ( as reported in Acta Phys. Sinica. 2021, 70(16): 163101), it was discovered that between the open-ring and closed-ring stable configurations, the potential energy curves of the electronic ground state (S0) and the first excited state (S1) exhibited an ‘X’ shape distribution along the reaction path. The conversion between open-ring and closed-ring occurs at the intersection of the potential energy curves, and a photoinduced ring-closing reaction accompanied by fluorescence was predicted, while a photoinduced ring-opening reaction was not. In this work, we apply the same method to investigate the mechanism of the photoinduced molecular switching process in the compounds of 2,3-di(3-thienyl)maleic anhydride(DTMA) and 2,3-di(3-pyrrolyl)maleic anhydride(DPMA). The transition state (TS) and minimum energy path (MEP) between the open-ring and closed-ring were determined by using the nudged elastic band (NEB) method. The potential energy curves of the lowest eight single excited states of DxMA(x = F, T, P) were computed based on the molecular configurations corresponding to the MEP curve (ground state S0). Interestingly, only the first excited state (S1 state) has a minimum value in the TS configuration among all eight excited states. That is, between the open-ring and closed-ring, the potential curves of S0 and S1 display an ‘X’ shape with a cross occurred at the TS configuration. The calculation of the S1←S0 resonance vibronic absorption spectrum of the open-ring/closed-ring state via molecular dynamics reveals that the transition intensity of the closed-ring state is 3 ∼ 5 times that of the open-ring state, which demonstrates that the efficiency of the closed-ring to the open-ring is higher.